The present invention relates to a scanning probe microscope used in applications such as measuring surface profile data of semiconductors, and to a method of measuring surface profile data using the scanning probe microscope.
The importance of semiconductor inspection and measurement technology and defect-analyzing technology in semiconductor-manufacturing processes is growing with the continued progress of finer circuit patterning, associated with increases in the integration densities of semiconductor circuits. Using a scanning probe microscope (SPM) in surface profile data measurement of semiconductors is widely known as a technique for measuring surface profile data of samples to an accuracy of the atomic order of magnitude by scanning the surface of each sample with the very small tip of a probe being kept in close proximity to or in intermittent contact with the surface.
During the surface profile data measurement with SPM, whereas inspection regions are limited to confined regions down to square of several-hundred micrometers, a mechanical section for scanning with the probe is required to be of high positioning accuracy. Either a tubular three-dimensional driving mechanism constructed by combining a plurality of piezoelectric elements cylindrically, or a tri-pod three-dimensional driving mechanism constructed by tri-axially combining piezoelectric rods of the stacked type has been employed as the mechanical section for positioning the probe of the scanning probe microscope very accurately on a sample.
These probe-driving mechanisms, however, have the drawback that they structurally cause circular arc errors during probing. At the same time, the straightness of probe-driving axes also deteriorates since the force needed to drive one scanning axis affects the other two axes for structural reasons. As SPM-based measuring accuracy improves, the effects upon the other two axes may appear more obviously as distortions of three-dimensional images.
In addition, although SPM has an advantage that data on the stereographic surface profiles of samples can be measured with a high resolution of about 0.1 nanometer, sufficient measuring throughput cannot be obtained since SPM requires time-consuming operations during the determination of measuring positions on the surface of the sample and/or during the measurement. In semiconductor-manufacturing lines, therefore, SPM has been mainly used to analyze defects off-line, not in-line (during manufacturing processes).
However, if it is possible to detect the abnormality of various process apparatus immediately from SPM-based measurement results and feed back detection results to the processing parameters required for the process apparatus, the manufacturing yield in the particular semiconductor-manufacturing line can be improved by minimizing the manufacture of defective products. The implementation of in-line SPM is therefore anticipated. In the realization of in-line SPM, it is an important factor how many measuring positions can be processed (measured) per unit time, and a processing time of 20 seconds or less per position is required for current semiconductor-manufacturing lines. This processing time is equivalent to 30 wafers per hour (wph) in terms of measuring throughput.
Examples of such a probe-driving mechanism for improving the positioning accuracy of a probe include the three-dimensional scanning mechanism disclosed in Patent Reference 1. This probe-driving mechanism uses three voice coil motors to drive a tri-axis stage constructed by forming, in a Y-stage connected to an outer frame via resilient members, an XZ stage (X-Z combination stage) connected to the Y-stage via resilient members.
All stages are integrally formed using the same member, and the driving force of an independent voice coil motor is transmitted to each stage via a spindle. This probe-driving mechanism is constructed so that regardless of the displacement of the associated stage, each spindle is always pressed against the stage in parallel to the operating direction thereof. For example, when only the Y-stage operates, all resilient members connecting the Y-stage to the outer frame equally undergo elastic deformation and thus prevent unnecessary force from being applied to operation axes other than the Y-axis. In this way, the probe-driving mechanism is realized that can control probe positioning independently for each of the three axes and with high accuracy.
Also, Patent Reference 2 proposes a uniaxial parallel flat-plate-type micro-moving mechanism having resilient members and piezo-driving elements in combination. This mechanism is constructed by forming a fixed section (outer frame) and a movable section (stage) into a single unit via elastic deformation sections and inserting stacked piezo-elements between the outer frame and the stage to fix the integrally formed unit. The rotational components (circular arc errors) occurring in the moving direction of the stage can be eliminated since the movement of the stage is limited to the deforming direction of the elastic deformation sections. Combining more than one uniaxial micro-moving mechanism proposed in Patent Reference 2 allows an SPM probe-driving mechanism to be constructed.
In addition, Patent Reference 3 discloses an SPM configuration for improvement of measuring throughput. This configuration improves the measuring throughput of the SPM by detecting the surface of a sample by means of an objective lens disposed directly above the probe, and an approach sensor constituted by a laser diode and a photodiode, and bringing the sample surface close to the tip of the probe at high speed to reduce the time required for the SPM to start measurements.
Patent Reference 4 also discloses specific examples of an approach sensor constructed for the same purpose as that described in Patent Reference 3. In the SPM configurations shown in Patent References 3 and 4, since an objective lens is disposed directly above the probe contact position on the sample, it is possible to start measurements without moving the sample, after the measuring positions thereon have been determined using observation optics, and hence to improve the measuring throughput of the SPM.
[Patent Reference 1]
Japanese Patent No. 3544453
[Patent Reference 2]
Japanese Patent Laid-open No. 2004-191277
[Patent Reference 3]
Japanese Patent Laid-open No. 2003-202284
[Patent Reference 4]
Japanese Patent Laid-open No. 2004-125540